Probing the Dynamics of Methane in Metal-Organic Frameworks

Probing the Dynamics of Methane in Metal-Organic Frameworks

Probing the Dynamics of Methane in Metal-Organic Frameworks by Disk Chopper Spectrometer Group 3: Kai Gong, Tommy Harrelson, Ben Paren, Matthew Krafcik, Zhixia Li, Xiao Hu, Shuonan Chen NCNR Neutron Scattering Workshop | June 1923, 2017 Outl 1. Background ine Methane storage in metal-organic frameworks Why do we need to study the methane dynamics? 2. Materials & Methods How DCS works? Why DCS? 3. Preliminary Results Case 1: MOF-5 (rotational tunnelling modes, phonon density of states) Case II: UiO-66 (rotational tunneling modes)

4. Conclusions Title: Probing the Dynamics of Methane in Metal-Organic Frameworks by Disk Chopper Backgroun d Materials & Method Preliminary Results Conclusions Methane storage in porous metal-organic framework Methane (CH4) is a clean and naturally abundant source of energy Storing methane in porous media is actively pursued due to its high volumetric energy density Metal-organic framework is attractive dueto: Highly crystalline structure Nanometer-sized pores Ultrahigh porosities Functionalizable pore walls How strongly methane interact with the porous framework is critical

Too strong Too weak to Difficult to Difficult desorb adsorb Title: Probing the Dynamics of Methane in Metal-Organic Frameworks by Disk Chopper 3 Backgroun d Materials & Method Preliminary Results Conclusions Methane dynamics in metal-organic framework At high temperature, rotational diffusion dominates At low temperature, motions such as rotational tunneling dominate Dynamics of methane in the metal-organic framework the

interaction between methane and the metal organic framework Title: Probing the Dynamics of Methane in Metal-Organic Frameworks by Disk Chopper 4 Background Materials & Method Preliminary Results Conclusions Case 1: MOF-5 Metal connector Organic linker MOF-5 crystal unit cell Location of CH4 adsorption in MOF-5 Title: Probing the Dynamics of Methane in Metal-Organic Frameworks by Disk Chopper

5 Materials & Method Background Preliminary Results Conclusions Case II: UiO-66 Organic linker Metal connector UiO-66 crystal unit cell Zr6O4(OH)4 Cavka et al. J. Am. Chem. Soc. 2008 Location of CH4 adsorption in UiO-66

Title: Probing the Dynamics of Methane in Metal-Organic Frameworks by Disk Chopper 6 Background Materials & Method Preliminary Results Conclusions Disc Chopper Spectrometer: schematic view Optical Filter Sample Chamber Crystal Filter Monochromatic Beam Monitor White Beam Monitor Neutron Guide Shutter

Frame Overlap Chopper Order Removal Choppers Pulsing Choppers Monochromating Choppers Transmitted Beam Monitor Radial Collimator Sample Argon gas-filled Flight Chamber Beam Stop 913 3He detectors, 400x31x11mm3 Title: Probing the Dynamics of Methane in Metal-Organic Frameworks by Disk Chopper 7 Materials & Method Background

Preliminary Results Conclusions Why DCS? 25meV Intensity 1meV Resolution Title: Probing the Dynamics of Methane in Metal-Organic Frameworks by Disk Chopper 8 Backgroun d Materials & Method Case 1: MOF-5 tunnelling modes

Preliminary Results Conclusions CH4 rotational Measurement conditions: 1.5 K, 9 (~1meV) Fitted with 5 Gaussians on each side of the elastic peak 5 transitions between energy levels Title: Probing the Dynamics of Methane in Metal-Organic Frameworks by Disk Chopper 9 Backgroun d Preliminary Results Materials & Method Case 1: MOF-5 tunnelling modes Conclusions CH4 rotational 2 1

4 5 3 h= -30.27eV; h4= -7.83eV Transition energy is used to calculate the barrier energy Vbarrier = 23 meV; Vbarrier2 = 17.2 meV Energy barrier calculated from DFT-D: VDFT = 46 meV; VDFT2 = 28 meV 10 Title: Probing the Dynamics of Methane in Metal-Organic Frameworks by Disk Chopper Backgroun d Materials & Method Case 1: MOF-5 states Experiment calculation Preliminary Results Conclusions

CH4 phonon density of vs DFT 1.81A 25meV 11 Title: Probing the Dynamics of Methane in Metal-Organic Frameworks by Disk Chopper Backgroun d Materials & Method Case 1I: UiO-66 tunnelling modes Preliminary Results Conclusions CH4 rotational UiO-66 MOF-5 12

Title: Probing the Dynamics of Methane in Metal-Organic Frameworks by Disk Chopper Backgroun d Materials & Method Preliminary Results Case 1I: UiO-66 tunnelling modes Conclusions CH4 rotational 5 Peak No. 3 6 4 2 1

Avg Area Ratio 1 0.0029605 1.0000 2 0.0100795 3.6529 3 0.025015 8.3910 4 0.014495 6.0513 5 0.003705 6.4205 6 0.003795 1.2946

Expected intensity ratio - 10:5:2:8:4 UiO-66: h = -30.5 eV; h4 = -2.6 eV MOF -5: h= -30.27eV; h4= -7.83eV h = -30.5 eV; h4 = -2.6 eVeV; h4 = -2.6 eV; h4 = -2.6 eV13eV Title: Probing the Dynamics of Methane in Metal-Organic Frameworks by Disk Chopper Backgroun d Materials & Method Preliminary Results Conclusions DCS allows for selectivity over a wide range of energies (eV-meV) DCS is powerful tool to probe CH4 dynamics in porous metal-organic framework. UiO-66 is more disordered than MOF-5 but similar rotational barriers. The results can be used to test DFT to improve the theory. The results can help improve methane storage

material development. h = -30.5 eV; h4 = -2.6 eVeV; h4 = -2.6 eV; h4 = -2.6 eV14eV Title: Probing the Dynamics of Methane in Metal-Organic Frameworks by Disk Chopper Acknowledgments Summer school organizers HFBS, DCS and MACS scientists Guest lecturers beamline NCNR staff Group 3 team members 15

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